Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Roadster rear suspension fail

I stand to be corrected, but from memory my S2 Roadster 4 seater wasn't fitted with ATB from new.

It was a bit of a handful in damp conditions and always experienced axle tramp if you accelerated quickly off the mark.despite having adjustable rear suspension dampers fitted.

John, is the 4seater a more heavy car?

I think it was about 50kgs heavier, also not helped by the spare wheel (and weight of the rear seats) being set further back from the rear axle compared to the 2 seater, which must also have impacted the balance/weight distribution of the car. Of course some of this would have been offset by having different rear springs.

Just back from a lovely twilight drive through the New Forest, it might be my imagination but the car seems to be going better than ever, without the ATB..... I will give it some time with different driving styles and in different road conditions, but so far I'm very happy ! Thanks everyone for all your helpful suggestions and technical gen.

I agree Heinz. That was the main point I made regarding the coil sprung 5 link rear, be it factory or SSL. Axle location (particularly needed under hard acceleration) is separated from the suspension medium.

In the OP's case I would still be influenced by the videos @mph posted though. Given enough power available and used, the unrestrained axle wind up could potentially cause damage and won't stop leaf spring action being compromised. Given this ATB's may be the lesser of two evils and hence why factory fitted.

Well who knows all the facts here as I'm sure it was a case of "oh the car is doing this" so MMC decided it was axle tramp caused by torque winding the rear axle, but if you look carefully at the video's posted there is no judder at the nose of the diff which is usually a good indicator of axle tramp. As Heinze said, there will always be some level of distortion to leaf springs. John, I'm surprised that with the extra load rear springs on the 4 seat version that you could get any wind up at all. Now we know that the BHP of the Roadster's was probably way to high for the chassis on a road going Mog, one of the reasons I chose not to go down that route, living in N.Wales with the slimy roads for ....well, most of the year, the Roadster really was a handful. and on the really narrow tight and winding stuff you were changing down two gears yet going up in singles and your hand never left the gear lever. So you end up screaming the engine in too low a gear just to keep your hands on the wheel. Then when you got a chance to open it up the rear wheels would spin in the first three gears without even trying. So I found I was driving the car not to have fun but to prevent undesirable effects happening.

So what might be the cause, In my humble opinion I think quite a bit of this is down to the tyres skipping as they loose traction, There just isn't enough sophistication or weight in combination to stop these effects happening. If we compare the Roadster to the plus 8, even with the narrow bodies, it lays down the power on the road much better. So perhaps the classic chassis'd cars had just about reached the sweet spot for road use and maximum power delivery on that chassis then. Yes, on the track everything is much more predictable. They have also had chassis and suspension changes to improve handling and wider grippier tyres, neither of which in value for money terms would greatly improve a classic for road enjoyment.

I think as so many have said, we should not lose sight of what a classic is and enjoy it for what it is warts and all. Of course there is now the option of a CX platformed car with its Mclaren like chassis and with used prices now hitting the £50,000 and under mark this would resolve a lot of those seeking a desire to remove these issues. I quickly decided I didn't want to go down that path, mainly because of the BMW association and I have previously gone into that in some depth so won't revisit it again here. However perhaps I hadn't realised fully on what I had fully based my decision. I had from being a boy always loved the Morgan 4's and when at too great an age I was able to make that happen, I was able to enjoy the full ownership experience, a lot of which consists of the maintenance, servicing and repairs to the car as well as driving it! And yes I like its quirks, that old fashioned driving style yet giving you the reliability of a much more youthful car. And when even my plus 4 shows a bit of chassis inadequacy I sort of like it! It's fast enough for me around the roads I drive and its different. I think what I mean is I bought it for exactly what it is and I really didn't want a porsche, ancient or modern. I too have had a period of getting caught up in trying to resolve issues with the classic chassis'd cars, yes you can improve them but not eradicate them. All that happens is you become more attuned to the issue and dwell on resolving it rather than enjoying the car for what it is. That said proper maintenance and servicing and understanding the chassis will make the car perform at its best!

Depending on the severity of the tramping , particularly from a standing start - without ATB’s you are in danger of overstressing the springs & taking the universal coupling at the rear out of its angular comfort zone. Bear in mind MMC haven’t got the best reputation for the quality of their leaf springs .

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In the end I reinstalled the ATB with the replacement zonking big bolt (thanks to Rutter's). Not an easy job. Can't say as it has made any discernible difference, but it's now back together the way it left the factory. At least I now know what the markings on bolt heads mean https://www.aftfasteners.com/grades-of-bolts-bolt-grade-markings-bolt-strength-chart/

For fear of stating the obvious, as swing shackles are an essential component part of any leaf sprung suspension system, and on a traditionally chassis Morgan we have rear mounted swing shackles, when the rear suspensions is under compression a Morgan axle not only rises, as the leaf spring flattens and so lengthens it also must also be allowed to roll backwards with the shackles.

If you fit a rigid bar tying the axle directly to the chassis, the axle can no longer roll back, the anti-tramp bar used by Morgan is just this, it is also therefore no different to removing the rear spring shackle and replacing it with a fixed pivot point on the chassis. Swing shackles exist for a reason, removing them or fitting a rigid bar tying the axle to the chassis (essentially the same thing) is to completely ignore the natural flattening and disregard the consequent lengthening of the leaf springs under compression.

In such a setup the poor leaf spring ceases to function as a spring, compression loads are now effectively moved along the spring length end to end, it will therefore largely function as a solid bar itself. Of course the Morgan ant-tramp bar is not strictly speaking fully rigid, while it does have pivots at both ends these should be ignored as they will have no effect on the compression and expansion loads placed on the bar as the axle attempts to roll back and forth, so the only reason the Morgan ant-tramp bar is not fully rigid is because it's been fitted with a big rubber bush.

It's quite clear all the compression and expansion loads on the bar will be directly transferred to the bush, as such it's astonishing the bush and or the chassis mounting point for the anti-tramp bar lasts longer than a few hundred miles! I would imagine what saves the system is the very short travel of the Morgan rear suspension, this in itself is a function of placing the rear axle over the flat chassis rather than the common solid axle design practice of placing the axle under the chassis that is also arch shaped at this point to allow for axle movement under compression.

For sure, if the Morgan axle could move any more than the very limited amount it does, the anti-tramp bar bush and or its chassis mounting point would have very short lives indeed.

To understand why Morgan chose to horribly limit the rear suspension travel by placing the axle above the flat chassis, we must travel back in time to the early 1930's when the 'Low Chassis' look became fashionable, by placing the axle over the chassis car makers such as Invicta (there were many others) could create a far lower and sleeker look.



Clearly Morgan/HFS were heavily influenced by the 'Low Chassis' fashion in the early 1930's when designing the 4/4.



However, in choosing to place the axle above the chassis, in a stroke HFS created the suspension travel and ground clearance issues that unbelievably we are still discussing on Talk Morgan today, some 90 years later!!!

Back to the Invicta S-Type Low Chassis, it's well documented that Donald Healey who raced the first of the breed was so concerned about the ground clearance of Noel Macklin's stylish under-slung design, that in preparation for the Rallye Monte-Carlo in the winter of 1931 he fitted larger wheels and higher cycle wings to give extra height over the snow-covered and deeply rutted roads.



Almost comically, the issues that so concerned Donald back in 1930 as he prepared his Invicta for the 31 Rallye Monte-Carlo, still persist in the trad chassis Morgan community to this day. I myself have decided to fit 205/65 tyres to replace Monty's soon to be worn out 185/65 tyres, not for the extra grip but for the additional 12mm of ground clearance they'll give.

It's not my idea though, it was Donald's some 95 years before

Fitting lowering blocks to Monty revealed the need to raise the top mounts for my new Bilstein rear dampers by 35mm, this is necessary to regain the precious little travel lost in the process of lowering the car. TBH it would have been nice if the Morgan suspension specialist had mentioned this when I purchased the Bilsteins from him, but sadly that wasn't the case

However, I strongly suspect the chronically poor travel this gave me is the reason my tuned 183 horsepower Duratec Plus 4 currently doesn't exhibit any axle tramp whatsoever, this despite there being no ant-tramp bars fitted. With the rear end riding on the Bilstein's bump stops the axle is simply unable to move enough to reveal any wind up.

However, when I finally raise the top damper mounts by 35mm I fully expect axle tramp to rear it's ugly head

To fix it I will not be fitting anti-tramp bars for the reasons I've mentioned above, the way I plan to solve any axle tramp that may potentially reveal itself is to fit what the Yanks call a diff snubber. A diff snubber is simply a rubber cone fitted to my now strengthened rear hoop that will progressively and softly limit pinion angle, using a threaded rod and lock nut arrangement will allow me to set the clearance between the rubber cone and the pinion casing, I can then adjust and fine tune the snubber's effect on limiting pinion angle.

Well that's the plan Donald, God rest your sole

Goodness. That's an excellent desription of what's happening in engineering terms, thanks. I had drawn the same conclusion regarding the seemingly illogical and pointless ATB (especially just one), but having re-fitted it at least I'm not now tripping over it on the bathroom floor where I had stored it. I may de-mount it again next spring when I've covered some more miles, but next time I will get a ratchet ring-spanner as getting to that bolt from above (I don' t have a ramp) is a pain.